Capillary electrophoresis MCQs With Answer

Capillary electrophoresis (CE) is a high-efficiency, small-volume separation technique central to modern pharmaceutical analysis. This blog presents carefully curated MCQs on Capillary Electrophoresis for M. Pharm students, covering principles, instrumentation, method development, and advanced modes such as MEKC, CIEF, and CE-MS. You will test your understanding of electroosmotic flow (EOF), electrophoretic mobility, buffer chemistry, capillary coatings, detection strategies, stacking techniques, and practical troubleshooting. Each question targets conceptual depth and real-world analytical decisions relevant to bioanalysis, chiral separations, peptide/protein profiling, and ionic drug assays. Review the explanations by focusing on the correct answer choices, and use these MCQs to sharpen both exam readiness and method development insight in CE.

Q1. In capillary zone electrophoresis (CZE), separation is primarily based on differences in:

• Hydrodynamic volume of analytes
• Electrophoretic mobility of analytes in an electric field
• Partition coefficients between micelles and bulk solution
• Vapor pressure of analytes

Correct Answer: Electrophoretic mobility of analytes in an electric field

Q2. The main origin of electroosmotic flow (EOF) in an uncoated fused-silica capillary is:

• Pressure differences between inlet and outlet vials
• Ionization of silanol groups forming an electrical double layer at the capillary wall
• Temperature gradients along the capillary
• Presence of organic modifiers in the buffer

Correct Answer: Ionization of silanol groups forming an electrical double layer at the capillary wall

Q3. Which change generally increases the magnitude of EOF in a fused-silica capillary?

• Increasing buffer pH (above the silanol pKa) to enhance wall deprotonation
• Increasing buffer ionic strength
• Lowering the capillary temperature
• Dynamic coating with a cationic surfactant such as CTAB

Correct Answer: Increasing buffer pH (above the silanol pKa) to enhance wall deprotonation

Q4. To minimize Joule heating during CE runs, a commonly used strategy is:

• Using a low ionic-strength buffer to limit current
• Applying the highest possible voltage
• Using a very short capillary with a large inner diameter
• Adding high concentrations of non-volatile salts

Correct Answer: Using a low ionic-strength buffer to limit current

Q5. Which statement about electrokinetic injection is TRUE?

• It provides mass-based injection independent of analyte mobility
• It favors injection of species with higher electrophoretic mobility and appropriate charge polarity
• It is unaffected by sample conductivity
• It eliminates matrix-related bias in trace analysis

Correct Answer: It favors injection of species with higher electrophoretic mobility and appropriate charge polarity

Q6. A practical approach to reverse EOF in a fused-silica capillary is to use:

• Dynamic coating with a cationic surfactant (e.g., CTAB) to render the wall positively charged
• Dynamic coating with an anionic surfactant (e.g., SDS)
• Very high ionic-strength phosphate buffers
• Increasing the capillary temperature

Correct Answer: Dynamic coating with a cationic surfactant (e.g., CTAB) to render the wall positively charged

Q7. To separate neutral analytes using capillary electrophoresis, a common method is to:

• Increase the applied voltage
• Add an anionic surfactant (e.g., SDS) above the CMC to perform MEKC
• Lower the pH below 2
• Use a pressure-driven flow only

Correct Answer: Add an anionic surfactant (e.g., SDS) above the CMC to perform MEKC

Q8. Which statement best describes capillary isoelectric focusing (CIEF)?

• Analytes are separated by size in a polymeric sieving matrix
• Proteins migrate in a pH gradient and focus at their isoelectric point (pI) where net charge is zero
• Neutral molecules partition between micelles and bulk buffer
• Analytes are separated based solely on hydrophobicity

Correct Answer: Proteins migrate in a pH gradient and focus at their isoelectric point (pI) where net charge is zero

Q9. For CE–MS coupling via ESI, the preferred background electrolyte is typically:

• Concentrated phosphate buffer with SDS
• Volatile ammonium acetate/formate buffers at low–moderate ionic strength
• High-concentration borate buffer (100 mM) with non-volatile salts
• Tris–HCl buffer with glycerol

Correct Answer: Volatile ammonium acetate/formate buffers at low–moderate ionic strength

Q10. In CZE (with adequate temperature control), increasing the applied voltage generally leads to:

• Longer migration times and decreased efficiency
• Shorter migration times and higher efficiency until limited by Joule heating
• No change in efficiency or analysis time
• Reversal of analyte migration order

Correct Answer: Shorter migration times and higher efficiency until limited by Joule heating

Q11. A common capillary preconditioning routine for uncoated fused-silica before CZE runs is:

• Flush with organic solvent only (e.g., acetonitrile)
• Flush with 0.1 M NaOH, then water, then running buffer
• Flush with concentrated phosphoric acid only
• No flushing is necessary between runs

Correct Answer: Flush with 0.1 M NaOH, then water, then running buffer

Q12. For fluorescently labeled analytes, the detector offering the highest sensitivity in CE is typically:

• On-capillary UV absorbance at 214 nm
• Laser-induced fluorescence (LIF)
• Refractive index detection
• Electrochemical amperometric detection

Correct Answer: Laser-induced fluorescence (LIF)

Q13. Field-amplified sample stacking (FASS) is most effective when:

• The sample is prepared in a higher-conductivity matrix than the BGE
• The sample is prepared in a lower-conductivity matrix than the BGE
• The BGE contains no ions
• The capillary is coated to eliminate EOF

Correct Answer: The sample is prepared in a lower-conductivity matrix than the BGE

Q14. In an uncoated fused-silica capillary at basic pH (EOF toward the cathode), the typical migration order is:

• Anions → Neutrals → Cations
• Neutrals → Cations → Anions
• Cations → Neutrals → Anions
• Neutrals → Anions → Cations

Correct Answer: Cations → Neutrals → Anions

Q15. Adding 20% methanol to the BGE in CZE typically:

• Increases EOF and current
• Decreases EOF and current due to higher viscosity and lower dielectric constant
• Has no effect on EOF but increases current
• Reverses the direction of EOF

Correct Answer: Decreases EOF and current due to higher viscosity and lower dielectric constant

Q16. A common approach for chiral separations in CE involves adding to the BGE:

• Chelating agents such as EDTA
• Cyclodextrin or derivatized cyclodextrins as chiral selectors
• High concentrations of phosphate salts
• Non-ionic polymers to increase viscosity only

Correct Answer: Cyclodextrin or derivatized cyclodextrins as chiral selectors

Q17. Decreasing the capillary inner diameter from 75 μm to 25 μm will most likely:

• Increase Joule heating and reduce allowable field strength
• Reduce Joule heating and permit higher electric fields but lower UV absorbance sensitivity
• Have no effect on heat dissipation or sensitivity
• Increase on-capillary UV pathlength and sensitivity

Correct Answer: Reduce Joule heating and permit higher electric fields but lower UV absorbance sensitivity

Q18. Increasing the ionic strength of the running buffer generally:

• Increases EOF by increasing zeta potential
• Decreases EOF by compressing the electrical double layer
• Does not affect EOF
• Reverses EOF direction

Correct Answer: Decreases EOF by compressing the electrical double layer

Q19. A key advantage of contactless conductivity detection (C4D) in CE is that it allows:

• Highly sensitive detection of only fluorescent compounds
• Direct detection of inorganic ions and small ions lacking chromophores
• Operation only at very high pH
• Elimination of buffer conductivity effects

Correct Answer: Direct detection of inorganic ions and small ions lacking chromophores

Q20. Capillary gel electrophoresis (CGE) is primarily used to separate biomolecules based on:

• Hydrophobicity
• Charge only
• Size via a polymeric sieving matrix (e.g., DNA fragment analysis)
• Vapor pressure differences

Correct Answer: Size via a polymeric sieving matrix (e.g., DNA fragment analysis)

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